User:Miaomin Zhang/Sandbox 1

One of the CBI Molecules being studied in the University of Massachusetts Amherst Chemistry-Biology Interface Program at UMass Amherst and on display at the Molecular Playground.

S-adenosylmethionine-dependent protein methyltransferase, CheR
Molecular Playground Banner: CheR, the protein that reactivates numb bacterial "noses"

Bacteria such as Salmonella typhimurium use chemotaxis system to swim towards neutrients and other attractants. At the forefront of the chemotaxis system are a set of transmembrane proteins called chemoreceptors. They sense the chemical environment and trigger the chemotaxis signal transduction pathway, which eventually affect the flagella motors, causing bacteria to either keep moving up the gradient (if they are on the right track) or stumble to change directions. However, the binding between attractants and chemoreceptors also suppresses the receptor activity and reduces the tumbling frequency. An adaptation mechanism is therefore needed to restore chemoreceptors' activity to elicit flagella responses. This is provided by reversible methylation of specific glutamate residues in the chemoreceptors' cytoplasmic domains, where methylation is catalyzed by S-adenosylmethionine-dependent protein methyltransferase, CheR.



CheR binds to a specific sequence at the C-termini of chemoreceptors through noncovalent interactions like hydrogen bonds and methylates neighboring receptor molecules. The 3D structure on the right shows the S. typhimurium CheR protein in revolutionary conservation grade colors []. The green chain represents the C-terminal pentapeptide of the aspartate receptor (Tar) to which CheR is attached; and the methylation reaction product, S-adenosylhomocysteine (AdoHcy) that lies at center of CheR is shown in ball-and-stick model and CPK element colors. As seen from this scene, the active site of CheR is the most highly conserved part of the protein.